Image forming apparatus, which applies a lubricant to an image carrying member and presses a cleaning blade made of urethane rubber or the like against the image carrying member to scrape a developer remaining on the image carrying member, are publicly known. In the cleaning blade, a tip section abutting against the image carrying member is deformed to form a nip between the image carrying member and the cleaning blade.
When deformation of the tip section of the cleaning blade is large, a frictional force between the tip section and the image carrying member is large, and a location different from an inherent edge may be worn to fracture the tip section of the cleaning blade and a life of the cleaning blade may be shortened. Therefore, it is required to select a material in which an elongation percentage under tensile stress is low to a certain degree for the cleaning blade.
Conventionally, in selecting a material of the cleaning blade, the propriety of using as a material of a cleaning blade has been determined by stress (modulus) at which predetermined elongation is recorded in a tensile-elongation test. In Patent Document 1, 300% modulus (stress value at the time when elongation is 300%) is used as a measure of selecting a material of the cleaning blade. Further, in Patent Document 2, 100% modulus is used as a parameter to select a material of the cleaning blade.
However, in actual cleaning blades, since stress is nonuniformly distributed to act on the cleaning blade, it was impossible to correctly evaluate the suitability of a material as a cleaning blade by just the modulus. Consequently, in the conventional image forming apparatuses, a life of the cleaning blade might be shorter than a predicted life.    Patent Document 1: Japanese Unexamined Patent Publication No. 2003-58009    Patent Document 2: Japanese Unexamined Patent Publication No. 2006-267299